Liquid crystal display device and manufacture method thereof

ABSTRACT

A method of manufacturing a reflecting substrate in a liquid crystal display device is disclosed, comprising the steps of: (a) providing a substrate having a first metal layer, wherein the first metal layer is formed with at least one soft metal or the alloys thereof; and (b) forming an aluminum nitride layer on the first metal layer. The method of the present invention is capable of forming a rugged, shining, reflective layer on a transflective, or a reflection type TFT LCD with simple steps and low cost.

This application is a divisional application of pending U.S. applicationSer. No. 11/269,616 filed Nov. 9, 2005 (of which the entire disclosureof the pending, prior application is hereby incorporated by reference).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a LCD device and more particularly, toa LCD device with rugged, shining, reflective layer.

2. Description of Related Art

LCD devices are usually available in four types: reflective type,transflective type, projective type and transmissive type. Other thanreflective type, most LCD devices are transmissive type. The lightsource of this type mainly depends on the backlight behind the liquidcrystal panel to make the LCD visible. Due to limited brightness, thescreen becomes blur and invisible when exposed to sunlight directlybecause the sunlight reflected from the surface of the screenovershadows the images formed on the LCD.

The reflective type LCD doesn't emit light itself but becomes bright byreflecting the light coming into the liquid crystal panel by way of areflective substrate rather than glowing by itself. Because theelemental principle of brightness of the reflective type LCD isdifferent from that of the transmissive type LCD, the reflective typeLCD does not need backlight or build-in illumination. Moreover, thebrightness of the reflective type LCD can be provided by external lightsources such as artificial light or natural light. Therefore, thebrighter the external light source is, the brighter the reflective typeLCD is, and the better the reflective type LCD for outdoor use will be.In addition, because less power for reflective type LCD consumes, thisLCD device can be lighter, thinner and more energy-saving and moreconvenient for bright environment.

The conventional reflective type LCDs includes a layer of reflectivematerial, such as Al or Cr, formed over the surface of a bottomsubstrate, and a rugged or uneven surface is formed for enhancingreflectivity. If a smooth mirror used as a reflective plate is attachedto the back inner wall of the manufactured liquid crystal cell, anobserver may look at his/her own image on the LCD panel. This is called“mirror reflective phenomenon.” If the pattern over the reflective plateis in a shape of regular concave and convex wave, the reflected lightwill be in various colors even though the incident light is white. Thesurface of the reflective plate resembles the diffraction grating of aspectrometer and produces the same phenomenon. To solve the problem,i.e. to avoid the associated phenomenon of the reflective angle and thewavelength, the surface of the reflective plate is required to beirregularly roughened. The reflective light then includes concurrentlypositive reflective light and diffused reflective light.

Doriguzzi et al., in U.S. Pat. No. 4,106,859, disclosed a method formanufacturing a rugged surface of an organic layer, particularly acasting method. An even organic layer 120 is roughened under pressure Pwith a rugged grooved mold 110 to form an irregular surface as shown inFIG. 1 a; or as shown in FIG. 1 b, an even organic layer 120 isroughened by a cylindrical mold 130 with rugged surface via rolling toprovide an irregular surface. Other than the method of casting,Komatsubara et. al. in U.S. Pat. No. 4,519,678 disclosed another method,comprising: forming a projection pattern 210 over a substrate 200;applying a polymer resin layer 220 and a reflective metal film 230 onthe projection pattern and the substrate. As shown in FIG. 2, a metalfilm with rugged surface is thus completed.

In addition, Oh et. al. in U.S. Pat. No. 5,917,567 disclosed yet anothermethod for forming a rugged surface, as shown in FIG. 3 a-c. First, aplurality of spacers 321 and a polymer solution 322 are sufficientlymixed. Then, a thin layer of the polymer solution 322 containing thespacers 321 is applied on a substrate 320 by spin coating, and baked toform a thin layer of rough surface. The pixel electrode 324 withreflective character, made of material such as Al or Ag, is formedthereon by sputtering. This results in pixel electrode 324 with ruggedsurface. Alternatively, prior to a polymer solution 322 beingdistributed and baked to form a rough surface, a plurality of spacers321 may be deposited over the substrate 320 first.

However, the foregoing methods require mechanical casting or thepresence of spacers to form a rough surface. A reflective metal filmcannot be formed unless a rough surface is formed first. They allinvolve tedious procedures and are not ideal for mass production. Surelyone single step for forming a reflective metal film with rough surfacewill dramatically reduces the time and labor cost for the production.

SUMMARY OF THE INVENTION

The present invention provides a method for manufacturing a reflectingsubstrate, especially for use in manufacturing metal films with a roughsurface. The atomic cells in the lattice are altered in the presence ofnitrogen atoms, and due to the existence of nitrogen atoms, it makes thesurface of the metal layer uneven because of twisted atomic cells in themetal lattice caused by inner repulsion once nitrogen is added into themetal layer. This method is simpler and easier than that of the priorart.

The method of the present invention for manufacturing a reflectingsubstrate, including the steps of:

(a) providing a substrate with a first metal layer over a surface,wherein the first metal layer is formed with at least one soft metal orthe alloys thereof; and

(b) forming a layer of aluminum nitride on the first metal layer.

The process of the present invention then proceed to subsequentnecessary steps after the foregoing steps, or may proceed to step (c):

(c) removing the layer of aluminum nitride on the first metal layerbefore carrying out subsequent steps, such as the formation of atransparent conductive layer. Alternatively, a reflective layer mayoptionally be directly deposited on the rugged surface of aluminumnitride, and followed by subsequent steps. Because the reflectivestructure on the reflecting substrate is the first metal layer, thefirst metal layer is preferably light-reflective. In addition, numeroussoft metals, preferably Al, Ag, Ni, Cu and Pt, are suitable for thefirst metal layer, which can be any soft metals with reflectivecharacter. Additionally, in order to increase the adhesion between thefirst metal layer and the substrate, a buffer layer may be formedbetween the first metal layer and the substrate to prevent the firstmetal layer from stripping from the substrate during the subsequentsteps in a environment of extreme high temperature and high pressure.The buffer layer may be formed of any suitable material, preferably Ti,titanium nitride, Mo, Cr or the alloys thereof. In the method of thepresent invention, the method for forming the layer of aluminum nitridein the step (b) may be any deposition process, preferably by reactivesputtering or evaporating on an aluminum-containing surface. A thicknessof the layer of aluminum nitride is altered by process conditions,preferably 150 Å-1500 Å.

Please refer to FIG. 7. The liquid crystal display device of the presentinvention, comprising:

a bottom substrate 500 comprising a layer of first metal 510, a layer ofaluminum nitride 520, and a layer of reflective metal 530, wherein thelayer of aluminum nitride 520 is between the layer of first metal 510and the layer of reflective metal 530; the layer of first metal 510 andthe layer of reflective metal 530 have a rugged surface, and the firstmetal layer 510 is formed with at least one soft metal or the alloysthereof;

an upper substrate 600 comprising at least one transparent electrode610; and

a layer of liquid crystal 700 located between the bottom substrate 500and the upper substrate 600.

The soft metal for the LCD device of the present invention may be anysoft metal with reflective character, preferably Al, Ag, Ni, Cu and Pt.In addition, the upper substrate may further include a color filter 620deposed between the upper substrate 600 and the transparent electrode610. The transparent electrode 610 may be any suitable material, such asindium tin oxide or indium zinc oxide. The material of the liquidcrystal may be any liquid crystal material with dielectric anisotropy,such as positive dielectric anisotropy or negative dielectricanisotropy.

The LCD device of the present invention may optionally further includeany additional functional elements to enhance or improve the desiredfunctions. Preferably, data lines, scan lines, common lines andtransistors 540 are formed on or over the surface of the bottomsubstrate. These data lines and scan lines are arranged to interlaceeach other without direct electrical connection, and every two adjacentdata lines and every two adjacent scan lines define a pixel area. In agiven pixel area, one of the data lines on the border of the pixel areais connected to a source 542 of a thin film transistor 540 inside of thepixel area; one of the scan lines on the border of the pixel area isconnected to a gate 543 of the thin film transistor inside of the pixelarea; and the pixel electrode is connected to the drain 541 of the thinfilm transistor 540 in the same pixel area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a-b is a cross-sectional view of prior art.

FIG. 2 is a cross-sectional view of prior art.

FIG. 3 a-c is a cross-sectional view of prior art.

FIG. 4 is a cross-sectional view of a first preferred embodiment of thepresent invention.

FIG. 5 is a cross-sectional view of a second preferred embodiment of thepresent invention.

FIG. 6 is a cross-sectional view of a third preferred embodiment of thepresent invention.

FIG. 7 is a cross-sectional view of a LCD device of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION First Preferred Embodiment

Please refer to FIG. 4(a). First, a substrate 10 is provided. In thisembodiment, the substrate is a glass substrate 10. Then, a layer ofthick metal 20 as a first metal layer is deposited on the substrate 10.The metal layer is made of Al, or an Al-containing soft alloy,preferably a layer of Al in the preferred embodiment. In addition, inorder to increase the adhesion between the Al layer 20 and the substrate10, a buffer layer 11 is formed between the Al layer 20 and the glasssubstrate 10 to prevent the Al layer 20 from stripping from the glasssubstrate 10 during subsequent steps in an environment of extreme hightemperature and high pressure. The buffer layer is any suitablematerial, preferably Ti, titanium nitride, Mo, Cr or the alloys thereof.Ti layer 11 is preferred in this embodiment. The Al layer 20 is formedaccording to any deposition method or formation method. In thispreferred embodiment, sputtering is used. Then, as shown in FIG. 4(b), alayer of aluminum nitride 30 is formed above Al layer 20 in a vacuumsputtering chamber. The aluminum nitride layer 30 is formed according toany deposition method. In this preferred embodiment, the aluminumnitride layer 30 is formed by reactive sputtering under nitrogenatmosphere.

As the aluminum nitride forms, the nitrogen atoms insert in the latticeof the metal and consequently change the lattice of the metal. Theinsertion results in distortion of the metal lattice close to thesurface and the formation of rugged surface of the Al metal 20. Therugged surface can be used as a base for the formation of subsequentreflective layer, conductive layer, or other layers.

In this embodiment, finally, a transparent conductive layer 50 such asITO, IZO is directly formed on the aluminum nitride layer 30, as shownin FIG. 4(c).

Preferred Embodiment 2

Because aluminum nitride layer 30 does not possess desirable reflectivecharacter, a reflective layer 40 is formed above aluminum nitride layer30 in this embodiment.

Referring to FIG. 5(a), a Ti layer 11 functioned as buffer layer and anAl layer 20 are deposited on a glass substrate10 in order. Then, asshown in FIG. 5(b), a aluminum nitride layer 30 is formed above the Allayer 20 by sputtering deposition in a vacuum sputtering chamber, andthe resultant Al layer 20 has a rough surface.

A reflective layer 40 is directly formed above the aluminum nitridelayer 30. In this embodiment, the reflective layer 40 is made of Al.Finally, a transparent conductive layer 50 such as ITO, IZO is formedabove the reflective layer 40, as shown in FIG. 5(c).

Preferred Embodiment 3

Alternatively, after the aluminum nitride layer 30 is formed, thealuminum nitride layer 30 is removed to reveal an Al layer 20 with roughsurface to function as reflective layer to proceed with any suitablesubsequent procedure.

Referring to FIG. 6(a), a glass substrate 10 is provided. Then a Tilayer 11 as buffer layer and an Al layer 20 are deposited on thesubstrate10 in order. Afterwards, as shown in FIG. 6(b), a aluminumnitride layer 30 is formed on the Al layer 20 by sputtering depositionin a vacuum sputtering chamber. Similarly, when the aluminum nitridelayer 30 is deposited on the Al layer 20, an irregularly rough surfaceis formed due to the presence of nitrogen atoms inserted among the Alatoms. After the aluminum nitride layer 30 is removed, the surface of Allayer 20 remains rough, as shown in FIG. 6(c). In this embodiment, thealuminum nitride layer 30 is removed by etching. Finally, a transparentconductive layer 50 such as ITO, IZO is formed on the roughened Al layer20, as shown in FIG. 6(d).

Although the present invention has been explained in relation to itspreferred embodiments, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1-7. (canceled)
 8. A liquid crystal display device, comprising: a bottomsubstrate comprising a layer of first metal, a layer of aluminumnitride, and a layer of reflective metal, wherein the layer of aluminumnitride is between the layer of first metal and the layer of reflectivemetal; the layer of first metal and the layer of reflective metal have arugged surface, and the first metal layer is formed with at least onesoft metal or the alloys thereof; an upper substrate comprising at leastone transparent electrode; and a layer of liquid crystal located betweenthe bottom substrate and the upper substrate.
 9. The liquid crystaldisplay device of claim 8, wherein the upper substrate further comprisesa color filter deposited between the upper substrate and the transparentelectrode.
 10. The liquid crystal display device of claim 8, wherein thesoft metal is Al, Ag, Ni, Cu or Pt.
 11. The liquid crystal displaydevice of claim 8, wherein the transparent electrode is made of indiumtin oxide or indium zinc oxide.
 12. The liquid crystal display device ofclaim 8, wherein the liquid crystal is positive dielectric anisotropicor negative dielectric anisotropic.